NASA's Chandra X-ray Observatory survey of nearby sun-like stars
suggests there is nearly three times more neon in the sun and local
universe than previously believed. If true, this would solve a critical
problem with understanding how the sun works.

"We use the sun to test how well we understand stars and, to some
extent, the rest of the universe," said Jeremy Drake of the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "But in
order to understand the sun, we need to know exactly what it is made
of," he added.

It is not well known how much neon the sun contains. This is critical
information for creating theoretical models of the sun. Neon atoms,
along with carbon, oxygen and nitrogen, play an important role in how
quickly energy flows from nuclear reactions in the sun's core to its
edge, where it then radiates into space.

The rate of this energy flow determines the location and size of a
crucial stellar region called the convection zone. The zone extends from
near the sun's surface inward approximately 125,000 miles. The zone is
where the gas undergoes a rolling, convective motion much like the
unstable air in a thunderstorm.

"This turbulent gas has an extremely important job, because nearly all
of the energy emitted at the surface of the sun is transported there by
convection," Drake said.

The accepted amount of neon in the sun has led to a paradox. The
predicted location and size of the solar convection zone disagree with
those deduced from solar oscillations. Solar oscillations is a technique
astronomers previously relied on to probe the sun's interior. Several
scientists have noted the problem could be fixed if the abundance of
neon is in fact about three times larger than currently accepted.

Attempts to measure the precise amount of neon in the Sun have been frustrated by a quirk of nature; neon atoms in the Sun give off no signatures in visible light. However, in a gas heated to millions of degrees, neon shines brightly in X-rays. Stars like the sun are covered in this
super-heated gas that is betrayed by the white corona around them during
solar eclipses. However, observations of the sun's corona are very
difficult to analyze.

To probe the neon content, Drake and his colleague Paola Testa of the
Massachusetts Institute of Technology in Cambridge, Mass., observed 21
sun-like stars within a distance of 400 light years from Earth. These
local stars and the sun should contain about the same amount of neon
when compared to oxygen.

However, these close stellar kin were found to contain on average almost
three times more neon than is believed for the sun. "Either the sun is a
freak in its stellar neighborhood, or it contains a lot more neon than
we think," Testa said.

These Chandra results reassured astronomers the detailed physical theory
behind the solar model is secure. Scientists use the model of the sun as
a basis for understanding the structure and evolution of other stars, as
well as many other areas of astrophysics.

"If the higher neon abundance measured by Drake and Testa is right, then
it is a simultaneous triumph for Chandra and for the theory of how stars
shine," said John Bahcall of the Institute for Advanced Study,
Princeton, N.J. Bahcall is an expert in the field who was not involved
in the Chandra study. Drake is lead author of the study published in
this week's issue of the journal Nature.